Wireless communication systems have become ubiquitous in society. Business and consumers use a wide variety of fixed and mobile wireless terminals, including cell phones, pagers, Personal Communication Services (PCS) systems, and fixed wireless access devices (i.e., vending machine with cellular capability). Wireless service providers continually try to create new markets for wireless devices and expand existing markets by making wireless devices and services cheaper and more reliable. To continue to attract new customers, wireless service providers are implementing new services, especially digital data services that, for example, enable a user to browse the Internet and to send and receive e-mail.
Many of these new services are made possible by the use of smart antenna arrays that transmit data from a base station to a mobile station using beam-forming techniques. Beam-forming focuses a transmit beam in the direction of a selected mobile station and, therefore, uses much less power than conventional transmission techniques that broadcast the data in all directions at equal strength. Moreover, since the beam is focused towards a selected mobile station, the signal power is greatly reduced in other directions, thereby reducing signal interference in other mobile stations.
However, in order to use beam-forming techniques, the direction of the mobile station must be known. A variety of conventional techniques are known for estimating the direction of a selected mobile station. In some direction-estimating devices, such as the Spatial Correlator from Metawave, the estimate is based entirely on the reverse (uplink) channel. It is then assumed that the forward (downlink) channel is similar to the reverse channel. However, it is well known that in real-world environments, this often is not true, due to reflected signals in the reverse channel. See generally, U.S. Pat. Nos. 6,108,565, 6,347,234, 6,330,460, 6,501,747, 6,233,466, and 6,320,853 and U.S. patent application Ser. No. 2002/0128027 A1. Another approach of the prior art proposes continuously sweeping a narrow beam over the entire sector. The mobile station must then synchronize with a narrow beam in a specific direction and transmit data after synchronization.
Unfortunately, the prior art techniques are not very accurate, since these techniques attempt to do direction finding with accuracy of up to 1 degree with a relatively wide beam width accuracy of about 15 degrees. Also, as indicated above, the prior art techniques determine the optimum forward link beam using reverse link measurements.
Therefore, there is a need in the art for improved wireless networks that are able to accurately transmit directed beams to a target mobile station. In particular, there is a need in the art for apparatuses and methods capable of accurately estimating the direction of a mobile station in order to optimize beam-forming techniques in the forward traffic channel.